This invention relates to a dust separator and, in particular, to an improved industrial dust separator capable of handling high inlet flow rates of light density materials, such as saw dust, paper dust and grain dust.
More specifically, this invention relates to a dust separator that utilizes a series of filter tubes for removing dust and other particulate materials from a high velocity airstream of process gas.
Dust collectors employing a plurality of filter bags are well known and used in the art for removing many kinds of airborne pollutants and contaminants from environmental air and other types of gases. Such collectors are manufactured by Griffin Environmental Co., Inc. of Syracuse, New York under the trade name Jet-Aire. In this type of installation, a series of elongated cylindrical air permeable filter bags are suspended from a tube sheet within an airtight housing. Contaminated air is brought into the bottom of the housing and allowed to flow upwardly towards an upper discharge opening above the tube sheets. The airstream is thus caused to flow inwardly through the filter bags before exiting the housing. Airborne particles and dust contained in the airstream are collected upon the outside surface of the filter bags. These particles agglomerate on the bag surfaces and, if not removed by some means, block the filters thereby adversely effecting the throughput and efficiency of the unit.
Material collected on the outside of the filter bags is generally removed by pulsing a reverse flow of high velocity air downwardly into the tubes. An air header is suspended over the bag openings which contains a series of nozzles for directing high velocity air directly into each bag. The air velocity is high enough to dislodge the accumulated particles from the outside surface of the bags and drive them downwardly into a hopper from which they are transported out of the system.
These multiple bag collectors have proven to be reliable units in the field. However, because of the upwardly directed flow pattern through the unit, the loading capacity of the filters is generally limited to between two and seven cfm of entering air for each square foot of filter bag area. Accordingly, the maximum upward flow rate that the unit can handle is generally restricted to about three hundred feet of air per minute. At these relatively low flow velocities, fine particles, such as sawdust, paper fibers and the like, have a tendency of collecting in static pockets throughout the bag housing and oftentimes build up to a point where the accumulated material bridges the gap between the bags. Once this happens, the flow through the housing is greatly reduced and will remain so until such time as the bridge is removed.
It should be further noted that these "reverse flow" prior art collectors require additional equipment and controls to periodically blow down the filter bags. Each bag must be supported internally with a wire mesh cage to prevent it from being collapsed by the process air that is being drawn inwardly. Typically, the cages are about eight feet long and added headspace must be provided to facilitate their installation and removal. Finally, in these reverse flow units the blower is generally connected to the top of the unit by lengthy airtight ducts, thereby increasing the load demands on the blower motor.
Some units known as "afterfilters" are used in conjunction with larger separators to clean fine particles or dust from the exhaust emitted by the larger unit. The dust laden air or gas is typically drawn through closely packed filter tubes so that the fine particles are collected on the inside of the tubes. The fine particles tend to clog the filter pores and build up along the inside surfaces of the tubes again forming bridges inside the tubes. Mechanical shakers are used to break up and dislodge the agglomerates. Tube shakers are complex devices involving electrically controlled motors that are coupled to the tubes by various types of mechanical linkages. These devices are space consuming and relatively expensive to install and operate.